Optical device

ABSTRACT

An optical device in which a polymerizable liquid crystal material various optical characteristics of which is stable even against heating during manufacture of an optical apparatus such as an image display is cured. The optical device has a support and an optical functional layer made of a cured polymerizable liquid crystal material having a predetermined liquid crystal regularity and provided on the support. The optical device is characterized in that the optical device is subjected to a heat treatment at a predetermined temperature and in that the thickness decrease of the optical functional layer defined by (A−B)/A is 5% or less where A is the thickness of the optical functional layer after the heat treatment, and B is the thickness of the optical functional layer after the optical device is heated for 60 minutes at the heat-treatment temperature.

This is a Division of application Ser. No. 10/250,779 filed Jul. 9,2003, which in turn is a National Stage of PCT/JP02/11619 filed Nov. 7,2002. The entire disclosure of the prior application is herebyincorporated by reference in its entirety.

TECHNICAL FIELD

The present invention relates to a heat-resistant optical device which,even when heat is applied, is stable in various properties.

BACKGROUND ART

Optical devices, such as phase difference films and circularly polarizedlight controlling optical devices, are used, for example, in imagedisplay devices. In use, the optical device is in some casesincorporated in image display devices such as liquid crystal displaydevices. In the production of these image display devices, the assemblyis sometimes heated at 200° C. or above, for example, for the formationof a polyimide film used as an aligning film or for the formation of anITO film as a transparent electrode. Further, when the image displaydevice using the optical device is used as a display in the inside of acar, the image display device is exposed to sunlight and consequently issometimes heated by the sunlight to 100° C. or above. Therefore, theoptical device, such as the phase difference film, used in image displaydevices such as liquid crystal display devices is possibly heated to atemperature of 100° C. or above and in some cases to 200° C. or above,depending upon the order of the incorporation of the optical device orthe place where the Optical device is used.

On the other hand, in recent years, as described, for example, inJapanese Patent Laid-Open No. 100045/2001 and Published JapaneseTranslation of PCT Publication No. 508882/1998, Optical devices producedby polymerizing a polymerizable liquid crystal material have beenproposed. These optical devices are advantageous in that properties of aliquid crystal can be anchored or immobilized by polymerization and canbe used as a film. This has led to expectation of the development ofoptical devices to various applications.

Regarding optical devices such as phase difference films, JapanesePatent Laid-Open No. 2109/1993 discloses a stretched phase differencefilm possessing excellent heat resistance. Japanese Patent Laid-Open No.142510/1993 discloses an optical device comprising a thermallypolymerizable liquid crystalline polymer possessing excellent heatresistance. Further, Japanese Patent Laid-Open No. 133628/2001 disclosesa highly heat-resistant polarizing diffractive film comprising a liquidcrystal material which contains a polymeric liquid crystal and acrosslinkable material.

The optical device produced by polymerizing the polymerizable liquidcrystal material, however, suffers from a problem that, for example, inthe case of a cholesteric layer having cholesteric regularity, uponheating, a shift in center reflection wavelength disadvantageouslyoccurs. Therefore, as described above, in use, when the optical deviceis incorporated in an image display device such as a liquid crystaldisplay device, disadvantageously, the optical device can be used onlyin a site not exposed to heat during the production of the image displaydevice.

Further, the stretched phase difference film disadvantageously undergoesa change in phase difference level at 80° C. or above, particularly at100° C. or above, and, thus, when used, for example, in on-vehicle LCDs,poses an uneven display or other problems.

DISCLOSURE OF THE INVENTION

In view of the above problems of the prior art, the present inventionhas been made, and a main object of the present invention is to providean optical device in which a polymerizable liquid crystal materialvarious optical characteristics of which is stable even against heatingduring manufacture of an optical apparatus such as an image displaydevice is cured.

The above object can be attained by an optical device characterized bycomprising a support and an optical function layer provided on thesupport and formed by curing a polymerizable liquid crystal materialwhile retaining predetermined liquid crystal regularity, the opticaldevice having been heat treated at a predetermined temperature, saidoptical function layer having a percentage reduction in layer thickness,defined by (A−B)/A, of not more than 5% wherein A represents thethickness of the optical function layer after the heat treatment and Brepresents the thickness of the optical function layer after reheatingthe optical device at said heat treatment temperature for 60 min. Whenthe percentage reduction in layer thickness upon heating for 60 min atthe same temperature as the heat treatment temperature is within theabove defined range, for example, the change in retardation value in thecase of the use of the optical device as a phase difference plate andthe change in center reflection wavelength in the case of the use of theoptical device as a circularly polarized light controlling opticaldevice can be minimized. Therefore, even when the optical device isincorporated in various image display devices, the change in function ofthe optical device can be minimized.

In a preferred embodiment of the present invention, the polymerizableliquid crystal material contains a photopolymerization initiator. Thisis because, when the polymerizable liquid crystal material is cured, forexample, by ultraviolet light, the incorporation of aphotopolymerization initiator is preferred from the viewpoint ofaccelerating polymerization. Further, an optical function layer formedby curing a polymerizable liquid crystal material containing aphotopolymerization initiator can effectively develop the advantage ofthe present invention.

More preferably, the support is a supporting substrate having analigning ability. This is advantageous from the viewpoint of theprocess, because, when an optical function layer can be formed on asupporting substrate having an aligning ability and as such can be used,there is no need to perform the step of transfer and the like.

According to another aspect of the present invention, there is provideda retardation layer laminate characterized by comprising a support and aretardation layer provided on the support and formed by curing apolymerizable liquid crystal material while retaining nematicregularity, smectic regularity, or cholesteric regularity, saidretardation layer laminate having been heat treated at a predeterminedtemperature, said retardation layer having a percentage reduction inretardation, defined by (Ra−Rb)/Ra, of not more than 5% wherein Rarepresents the retardation value of the retardation layer after the heattreatment and Rb represents the retardation value of the retardationlayer after reheating the retardation layer laminate at said heattreatment temperature for 60 min. When the retardation layer laminate isincorporated in various image display devices, a change in retardationvalue upon heating within the above range poses no problem associatedwith the use of the retardation layer laminate.

In a preferred embodiment of the present invention, the polymerizableliquid crystal material comprises a photopolymerization initiator and apolymerizable liquid crystal monomer. More preferably, the polymerizableliquid crystal material having cholesteric regularity comprises aphotopolymerization initiator, a polymerizable liquid crystal monomer,and a polymerizable chiral dopant. The retardation value is a valueassociated with the thickness of the retardation layer. The change inthickness of the retardation layer upon heating is estimated to dependupon the amount of the residue of the photopolymerization initiator.Therefore, when the polymerizable liquid crystal material contains aphotopolymerization initiator, it is considered that the advantage ofthe present invention can be utilized.

More preferably, the support is a supporting substrate having analigning ability. This is advantageous from the viewpoint of theprocess, because, when a retardation layer can be formed on a supportingsubstrate having an aligning ability and as such can be used as aretardation layer laminate, there is no need to perform the step oftransfer and the like.

According to still another aspect of the present invention, there isprovided a circularly polarized light controlling optical devicecharacterized by comprising a support and a cholesteric layer providedon the support and formed by curing a polymerizable liquid crystalmaterial while retaining cholesteric regularity, said circularlypolarized light controlling optical device having been heat treated at apredetermined temperature, said cholesteric layer having a percentagechange in center reflection wavelength, defined by |λa−λb|/λa, of notmore than 5% wherein λa represents the center reflection wavelength ofthe cholesteric layer after the heat treatment and λb represents thecenter reflection wavelength of the cholesteric layer after reheatingthe circularly polarized light controlling optical device at said heattreatment temperature for 60 min. For example, when the circularlypolarized light controlling optical device is incorporated in an imagedisplay device such as a color filter, a change in center reflectionwavelength upon heating within the above range poses no problemassociated with the use of the circularly polarized light controllingoptical device.

In a preferred embodiment of the present invention, the polymerizableliquid crystal material comprises a photopolymerization initiator, apolymerizable liquid crystal monomer, and a polymerizable chiral dopant.The center reflection wavelength of the cholesteric layer depends uponthe helical pitch, and a change in layer thickness causes a change inhelical pitch. Accordingly, for the same reason as described above, thepolymerizable liquid crystal material preferably contains aphotopolymerization initiator.

More preferably, the support is a supporting substrate having analigning ability. This is advantageous from the viewpoint of theprocess, because, when a cholesteric layer can be formed on a supportingsubstrate having an aligning ability and as such can be used as thecircularly polarized light controlling optical device, there is no needto perform the step of transfer and the like.

According to a further aspect of the present invention, there isprovided a method for heat treating an optical device, characterized bycomprising the step of heat treating, at a predetermined temperature, anoptical device comprising a support and an optical function layerprovided on the support and formed by curing a polymerizable liquidcrystal material while retaining predetermined liquid crystalregularity, whereby heat resistance is imparted to the optical device.The heat treatment in the above temperature range can previously removeingredients which are removed at the time of heating of the inside ofthe optical function layer. Further, the degree of polymerization of thepolymerizable liquid crystal material (three-dimensional network) can beenhanced. Therefore, even when heating is carried out later, that is,even when heating is carried out, for example, in the production of animage display device, a change in layer thickness and, in its turn, achange in properties can be prevented. Thus, heat stability can beimparted to the optical function layer.

According to still another aspect of the present invention, there isprovided a method for heat treating an optical device, characterized bycomprising the step of heat treating an optical device comprising asupporting substrate and an optical function layer, provided on thesupporting substrate and formed by curing a polymerizable liquid crystalmaterial while retaining predetermined liquid crystal regularity, at orabove a temperature which corresponds to an isotropic layer beforepolymerizing the polymerizable liquid crystal material, whereby heatresistance is imparted to the optical device. Thus, the heat treatmentat or above a temperature which corresponds to an isotropic layer beforepolymerizing the polymerizable liquid crystal material can bringmolecules, which have not been fully polymerized (crosslinked), in theoptical device to a more stable state. Therefore, even when heating iscarried out in the production of an image display device or the like, achange in layer thickness and, in its turn, a change in properties canbe prevented and, consequently, heat stability can be imparted to theoptical function layer.

In the heat treatment method according to the present invention,preferably, the heat treatment is carried out for 10 to 60 min. The heattreatment for a period of time in the above defined range can provide anoptical function layer possessing better heat stability.

Further, the polymerizable liquid crystal material preferably contains aphotopolymerization initiator, because a change in layer thickness uponheating is considered to be related to the presence of the residue ofthe photopolymerization initiator present in the layer.

More preferably, the content of the photopolymerization initiator is notless than 1% by mass. When the content of the photopolymerizationinitiator in the above defined range can particularly utilize theadvantage of the present invention.

In a preferred embodiment of the present invention, the heat treatmentis carried out at a temperature between a temperature applied to theoptical device in the production process of an optical apparatus, inwhich the optical function layer is used later, and a temperature 10° C.above the temperature applied in the production process. For example,when the optical device is used in a liquid crystal display device,previous heat treatment of the optical device at a temperature between atemperature applied to the optical device in the production process ofthe liquid crystal display device and a temperature 10° C. above thetemperature applied to the optical device in the production process ofthe liquid crystal display device can remove ingredients which, if theprevious heat treatment is not carried out, are removed from the opticaldevice upon exposure to heat in the production process of the liquidcrystal display device. Therefore, subsequent heating in the productionof the liquid crystal display device does not pose a problem of layerthickness reduction or the like.

More preferably, the optical function layer is a retardation layer, thepolymerizable liquid crystal material comprises a polymerizable liquidcrystal monomer, and the liquid crystal regularity is nematicregularity, smectic regularity, or cholesteric regularity. When theoptical device is a retardation layer laminate, previous heat treatmentcan minimize a change in retardation value. When the liquid crystalregularity is cholesteric regularity, the polymerizable liquid crystalmaterial should contain a chiral dopant.

In this case, a construction may be adopted wherein the optical functionlayer is a cholesteric layer, the polymerizable liquid crystal materialcomprises a polymerizable liquid crystal monomer and a polymerizablechiral dopant, and the liquid crystal regularity is cholestericregularity. When the optical device is the circularly polarized lightcontrolling optical device, previous heat treatment can minimize achange in center reflection wavelength upon heating.

Further, a construction may be adopted wherein the polymerizable liquidcrystal material comprises a polymerizable liquid crystal monomer andthe molecule of the polymerizable liquid crystal monomer has apolymerizable functional group in its both ends.

Further, a construction may be adopted wherein the polymerizable liquidcrystal material comprises a polymerizable liquid crystal monomer and apolymerizable chiral dopant and the molecule of the polymerizable chiraldopant has a polymerizable functional group in its both ends. When themolecule of the polymerizable chiral dopant has a polymerizablefunctional group in its both ends, both ends of adjacent molecules arebonded in a three-dimensional network manner, that is, polymerization ina three-dimensional network manner (crosslinking) takes place. As aresult, an optical device having better heat resistance can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a step which is a part of theproduction process of an optical device according to the presentinvention, wherein numeral 1 designates a transparent substrate, numeral2 an aligning film, and numeral 3 a supporting substrate;

FIG. 2 is a diagram illustrating a step which is a part of theproduction process of an optical device according to the presentinvention, wherein numeral 4 designates a liquid crystal layer;

FIG. 3 is a diagram illustrating a step which is a part of theproduction process of an optical device according to the presentinvention, wherein numeral 5 designates ultraviolet irradiation;

FIG. 4 is a diagram illustrating a step which is a part of theproduction process of an optical device according to the presentinvention, wherein numeral 6 designates an optical function layer;

FIG. 5 is a diagram illustrating a step which is a part of theproduction process of an optical device according to the presentinvention, wherein numeral 7 designates heat and numeral 8 an opticaldevice; and

FIG. 6 is a diagram illustrating a step which is a part of theproduction process of an optical device according to the presentinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

The optical device according to the present invention will be firstdescribed, and a heat treatment method for providing the optical deviceaccording to the present invention will be then described.

<Optical Device>

The optical device according to the present invention is characterizedby comprising a support and an optical function layer provided on thesupport and formed by curing a polymerizable liquid crystal materialwhile retaining predetermined liquid crystal regularity, said opticaldevice having been heat treated at a predetermined temperature, saidoptical function layer having a percentage reduction in layer thickness,defined by (A−B)/A, of not more than 5% wherein A represents thethickness of the optical function layer after the heat treatment and Brepresents the thickness of the optical function layer after reheatingthe optical device at said heat treatment temperature for 60 min.

Thus, in the present invention, when the percentage reduction inthickness of the optical function layer upon reheating at the sametemperature as the heat treatment temperature for 60 min is in the abovedefined range, a change in various optical properties attributable to achange in layer thickness can be prevented. Therefore, the opticaldevice according to the present invention can also be used in aproduction process in which heat is possibly applied. This can realizethe development of the optical device to various applications. Regardingthe predetermined heat treatment temperature, when the supportingsubstrate is, for example, a polymeric stretched film, which will bedescribed later, the heat treatment temperature should be below thesoftening (deformation) temperature of the supporting substrate. Forthis reason, in this case, the heat treatment temperature is generallyabout 80 to 120° C. On the other hand, when the supporting substrate is,for example, a glass substrate, thermal decomposition of the opticalfunction layer formed on the supporting substrate takes place at atemperature below the deformation temperature of the supportingsubstrate. For this reason, in this case, the heat treatment temperatureis generally about 180 to 240° C.

The reason why the percentage reduction in thickness of the opticalfunction layer in the optical device according to the present inventionupon heating is small is believed to be as follows.

Specifically, in the conventional optical device using a polymerizableliquid crystal material, the polymerizable liquid crystal material hasbeen polymerized and anchored or immobilized while retaining apredetermined liquid crystal structure, and, in this state, is used. Insuch a state that the polymerizable liquid crystal material has beenpolymerized to provide a polymeric material, there is a possibilitythat, in addition to the polymeric material having a liquid crystalstructure, for example, the residue of the photopolymerization initiatorand impurities produced at the time of the polymerization reaction, thatis, products attributable to the photopolymerization initiator, arepresent. Such impurities are not chemically bonded to the main chain ofthe polymer formed as a result of the polymerization of the monomer orthe like and thus are highly likely to be removed from within theoptical function layer upon heating after the polymerization. When thematerial within the optical function layer is removed upon heating, thethickness of the optical function layer is of course reduced.

In the present invention, as described later, an optical device havingan optical function layer, from which impurities have been previouslyremoved, can be provided by previously heating the optical functionlayer at a predetermined temperature to remove impurities present withinthe optical function layer. Therefore, even when heat is applied later,a reduction in layer thickness can be kept in such a thickness reductionrange that does not adversely affect the performance of the opticaldevice.

The optical device according to the present invention undergoes nosignificant reduction in layer thickness upon heating and thus has thefollowing function and effect.

Specifically, for example, when the optical function layer is aretardation layer, the thickness of the optical function layer is avalue related to retardation value. On the other hand, when the opticaldevice according to the present invention is used as a circularlypolarized light controlling optical device and the optical functionlayer is a cholesteric layer (in the present invention, a layer withinwhich a liquid crystal material having cholesteric regularity has beenanchored is referred to as cholesteric layer), the center reflectionwavelength of the cholesteric layer depends upon the layer thickness(helical pitch). That is, in this case, a change in layer thicknesscauses a change in helical pitch.

Therefore, when the thickness of the optical function layer issignificantly reduced upon heating, the above important opticalproperties are disadvantageously significantly changed. In this case,when the optical device is used in an image display device, expectedoptical properties cannot be provided, making it difficult to use theoptical device. In the optical device according to the presentinvention, since the percentage reduction in layer thickness uponheating is in the above range, the change in optical properties of theoptical device upon heating can be significantly reduced. Therefore, theoptical device according to the present invention can be advantageouslysatisfactorily used, for example, in image display devices which arehighly likely to be exposed to heat in the production process thereof.

The above optical device will be described for each element.

1. Support

In the present invention, the support refers to a supporting substratehaving an aligning ability. When the optical function layer istransferred by the step of transfer, the support refers to a receivingobject, that is, an object for receiving the optical function layer.

<Supporting Substrate Having Aligning Ability>

The optical device according to the present invention comprises asupporting substrate having an aligning ability and an optical functionlayer provided on the supporting substrate and formed by curing apolymerizable liquid crystal material while retaining predeterminedliquid crystal regularity.

The supporting substrate having an aligning ability may be constitutedby a substrate which as such has an aligning ability. Alternatively, thesupporting substrate having an aligning ability may comprise an aligningfilm provided on a transparent substrate. The former will be descried asa first embodiment, and the latter as a second embodiment.

(1) First Embodiment

In the first embodiment, a substrate per se has an aligning ability andconstitutes the supporting substrate. Specifically, a stretched film maybe mentioned as the supporting substrate in the first embodiment. Whenthe stretched film is used, molecules of the liquid crystal material canbe aligned along the direction of stretch. In this embodiment, what isrequired for providing a supporting substrate is only to provide astretched film. Therefore, advantageously, this can highly simplify thestep of providing a supporting substrate. The stretched film may becommercially available one. If necessary, stretched films of variousmaterials may be formed.

Specific examples of films for stretched films include: films ofpolycarbonate-based polymeric materials, polyester-based polymericmaterials such as polyallylate and polyethylene terephthalate,polyimide-based polymeric materials, polysulfone-based polymericmaterials, polyether sulfone-based polymeric materials,polystyrene-based polymeric materials, polyolefin-based polymericmaterials such as polyethylene and polypropylene, polyvinylalcohol-based polymeric materials, cellulose acetate-based polymericmaterials, polyvinyl chloride-based polymeric materials, polymethylmethacrylate-based polymeric materials or other thermoplastic polymers;and films of liquid crystal polymers.

In the present invention, among others, polyethylene terephthalate (PET)films are preferably used, for example, from the viewpoints of a broadeffective stretch ratio range and high availability.

The stretch ratio of the stretched film used in the present invention isnot particularly limited so far as the aligning ability can bedeveloped. Therefore, even a biaxially stretched film can be used so faras the stretch ratio in one axis is different from that in the otheraxis.

The stretch ratio significantly varies depending upon materials used andis not particularly limited. However, in the present invention, thestretch ratio is generally about 150 to 300%, preferably 200 to 250%.

(2) Second Embodiment

In the second embodiment, the supporting substrate having an aligningability comprises a transparent substrate and an aligning film providedon the transparent substrate.

The second embodiment is advantageous in that the direction of aligningcan be selected from a relatively wide aligning direction range byselecting the aligning film. Further, various aligning directions can berealized by selecting the type of a coating liquid, for aligning filmformation, to be coated onto the transparent substrate, and moreeffective aligning can be realized.

Aligning films commonly used, for example, in liquid crystal displayscan be suitably used as the aligning film in this embodiment. Ingeneral, a polyimide-based or polyvinyl alcohol-based aligning filmsubjected to rubbing treatment is suitable. Photoaligning films may alsobe used.

The transparent substrate used in this embodiment is not particularlylimited so far as the substrate is formed of a transparent material.Examples of transparent substrates include nonflexible transparent rigidmaterials, such as quartz glass, Pyrex (registered trademark) glass, andsynthetic quartz plates, or flexible transparent materials, such astransparent resin films and optical resin plates.

<Receiving Object>

The receiving object used in the present invention may be properlyselected depending upon applications of the optical device. In general,however, the use of a transparent material, that is, a transparentsubstrate, is suitable.

This transparent substrate may be the same as that described in theabove column of “Supporting substrate having aligning ability,” and,thus, the description thereof will be omitted.

2. Optical Function Layer

The optical device according to the present invention comprises theabove supporting substrate and an optical function layer provided on thesupporting substrate and formed by curing a polymerizable liquid crystalmaterial while retaining predetermined liquid crystal regularity. Theoptical function layer comprises a polymerizable liquid crystal materialwhich constitutes a polymeric material having liquid crystal regularity.In some cases, residues of additives, such as photopolymerizationinitiators, contained in a coating liquid for liquid crystal layerformation which will be described later are also contained in theoptical function layer. The polymerizable liquid crystal material andthe additives will be described.

<Polymerizable Liquid Crystal Material>

Polymerizable liquid crystal materials usable in the present inventioninclude polymerizable liquid crystal monomers, polymerizable liquidcrystal oligomers, and polymerizable liquid crystal polymeric materials.Polymerizable liquid crystal materials, which as such have nematicregularity or smectic regularity, are generally used. However, thepolymerizable liquid crystal material is not particularly limited tothese only and may have cholesteric regularity. In order to impart thecholesteric regularity, when the polymerizable liquid crystal materialper se has nematic regularity or smectic regularity, a polymerizablechiral dopant may be further used. The polymerizable liquid crystalmaterial and the polymerizable chiral dopant will be described.

(1) Polymerizable Liquid Crystal Material

As described above, polymerizable liquid crystal materials usable in thepresent invention include polymerizable liquid crystal monomers,polymerizable liquid crystal oligomers, and polymerizable liquid crystalpolymeric materials. The polymerizable liquid crystal material is notparticularly limited so far as, when the polymerizable liquid crystalmaterial per se has formed a liquid crystal phase, the liquid crystalphase has nematic regularity, smectic regularity, or cholestericregularity. The presence of a polymerizable functional group at bothends of the molecule is preferred from the viewpoint of the productionof a highly heat resistant optical device.

Examples of such polymerizable liquid crystal materials includecompounds (I) represented by formula (1) and compounds which will bedescribed later. A mixture of two compounds covered by formula (1) mayalso be used as compound (I).

The polymerizable liquid crystal material may also be a mixture of twoor more compounds covered by formula (1) and the compounds which will bedescribed later.

In formula (1) which represents compound (I), R¹ and R² each represent ahydrogen atom or a methyl group, and X preferably represents a chlorineatom or a methyl group. a and b showing the chain length of the alkylenegroup as a spacer of compound (I) are preferably in the range of 2 to 9from the viewpoint of developing liquid crystallinity.

In the above embodiment, examples of polymerizable liquid crystalmonomers have been described. In the present invention, however, forexample, polymerizable liquid crystal oligomers and polymerizable liquidcrystal polymeric materials may also be used. Conventional polymerizableliquid crystal oligomers and polymerizable liquid crystal polymericmaterials may be properly selected and used.

(2) Chiral Dopant

In the present invention, when the above optical device is a circularlypolarized light controlling optical device, that is, when the opticalfunction layer is a cholesteric layer and the polymerizable liquidcrystal material has nematic regularity or smectic regularity, a chiraldopant should be added in addition to the polymerizable liquid crystalmaterial.

The polymerizable chiral dopant used in the present invention refers toa low-molecular compound which has an optically active site and amolecular weight of not more than 1,500. The chiral dopant is mainlyused for inducing a helical pitch in positive uniaxial nematicregularity developed by compound (I). So far as this object can beattained, any low-molecular compound may be used as the chiral dopantwithout particular limitation. Specifically, any low-molecular compoundmay be used so far as the compound is compatible in a solution or meltedstate with compound (I) or the above compound, does not sacrifice theliquid crystallinity of the polymerizable liquid crystal material, whichcan have nematic regularity, and can induce a desired helical pitch inthe nematic regularity. The presence of a polymerizable functional groupat both ends of the molecule is preferred from the viewpoint ofproviding highly heat resistant optical device. For the chiral dopantused for inducing a helical pitch in the liquid crystal, any chiralityshould be found at least in the molecule. The chiral dopant having anoptically active site incorporated in the liquid crystalline compositionaccording to the present invention is preferably a chiral dopant whichis significantly effective in inducing a helical pitch in the nematicregularity. Specifically, the use of low-molecular compounds (II)represented by formula (2), (3), or (4), which have axial asymmetry intheir molecule, is preferred.

In formula (2), (3), or (4) which represents chiral dopant (II), R⁴represents a hydrogen atom or a methyl group. Y represents any one offormulae (i) to (xxiv), preferably any one of formulae (i), (ii), (iii),(v), and (vii). c and d, which represent the chain length of thealkylene group, are preferably in the range of 2 to 9. When c and d areless than 2 or not less than 10, the liquid crystallinity is less likelyto be developed.

The optimal amount of the chiral dopant incorporated in thepolymerizable liquid crystal material according to the present inventionis determined by taking into consideration the helical pitch inducingability and the cholesteric nature of the finally obtained circularlypolarized light controlling optical device. Specifically, although theamount of the chiral dopant incorporated significantly varies dependingupon the polymerizable liquid crystal material used, the amount of thechiral dopant may be in the range of 1 to 20 parts by mass based on 100parts by mass in total of the polymerizable liquid crystal material.When the amount of the chiral dopant incorporated is below the lowerlimit of the above-defined amount range, in some cases, satisfactorycholesteric nature cannot be imparted to the polymerizable liquidcrystal material. On the other hand, when the amount of the chiraldopant incorporated is above the upper limit of the above-defined amountrange, the alignment of molecules is inhibited. This possibly adverselyaffects curing by the application of an actinic radiation.

In the present invention, the chiral dopant is not necessarilypolymerizable. When the heat stability and the like of the opticalfunction layer are taken into consideration, however, the use of apolymerizable chiral dopant, which can be polymerized with thepolymerizable liquid crystal material to anchor the cholestericregularity, is preferred. In particular, the presence of a polymerizablefunctional group at both ends of the molecule is preferred from theviewpoint of providing highly heat resistant optical devices.

<Photopolymerization Initiator>

In the present invention, a photopolymerization initiator is preferablyadded to the polymerizable liquid crystal material. For example, whenthe polymerizable liquid crystal material is polymerized by electronbeam irradiation, the use of a photopolymerization initiator is in somecases unnecessary. In the case of a generally used curing method, forexample, curing by ultraviolet (UV) irradiation, a photopolymerizationinitiator is generally used for polymerization acceleration purposes.

In addition to the photopolymerization initiator, a sensitizer may beadded in such an amount range that is not detrimental to the object ofthe present invention.

The photopolymerization initiator may be generally added in an amount of0.5 to 10% by mass to the polymerizable liquid crystal materialaccording to the present invention.

3. Liquid Crystal Regularity

In the present invention, an optical function layer formed by curing thepolymerizable liquid crystal material while retaining predeterminedliquid crystal regularity is used.

Nematic regularity, smectic regularity, and cholesteric regularity maybe mentioned as the liquid crystal regularity. When the optical deviceis a retardation layer laminate, the optical function layer has nematicregularity or smectic regularity. On the other hand, when the opticaldevice is a circularly polarized light controlling optical device, theoptical function layer has cholesteric regularity.

The regularity is basically determined by liquid crystal regularity,which the polymerizable liquid crystal material per se develops, andwhether or not a chiral dopant is used.

The liquid crystal regularity can be provided by forming, on asupporting substrate having an aligning ability, a layer, for liquidcrystal layer formation, comprising the above polymerizable liquidcrystal material and an optional polymerizable chiral dopant andallowing the molecules of the liquid crystal to align along the aligningability of the supporting substrate. The liquid crystal layer can beconverted to an optical function layer by applying an actinic radiationto the liquid crystal layer in such a state that the liquid crystalregularity is retained, thereby curing the liquid crystal layer.

4. Percentage Reduction in Thickness of Optical Function Layer UponHeating

The present invention is characterized in that the percentage reductionin thickness of the above optical function layer, when heated for 60 minat the same temperature as applied in the heat treatment of the opticaldevice, is not more than 5%, preferably not more than 3%, particularlypreferably not more than 1%. For example, in the case where the opticaldevice is a phase difference plate or a circularly polarized lightcontrolling optical device, when the percentage reduction in layerthickness is in this range, there is no fear of causing a significantchange in retardation value or center reflection wavelength, which areimportant optical properties of the optical device, even upon heating ofimage display devices or the like using the optical device in theproduction thereof. Therefore, the optical device according to thepresent invention can be used even in the case where the optical deviceis exposed to heat in a step after mounting the optical device.

5. Specific Embodiments of Optical Device

Specific embodiments of the optical device according to the presentinvention include a retardation layer laminate comprising a retardationlayer as the optical function layer and a circularly polarized lightcontrolling optical device comprising a cholesteric layer as the opticalfunction layer. The retardation layer laminate and the circularlypolarized light controlling optical device will be described.

<Retardation Layer Laminate>

In the present invention, when the optical device is a retardation layerlaminate, the retardation layer laminate may comprise a support and aretardation layer provided on the support and formed by curing apolymerizable liquid crystal material while retaining nematicregularity, smectic regularity, or cholesteric regularity, wherein thepercentage change in retardation value of the retardation layer, whenheated for 60 min at the same temperature as the predeterminedtemperature in the heat treatment, is not more than 5%, preferably notmore than 3%, particularly preferably not more than 1%.

Thus, in the optical device according to the present invention, thechange in layer thickness upon heating is so small that, when theoptical device is used as a retardation layer laminate, the change inretardation value upon exposure of the retardation layer laminate toheat is advantageously very small.

The retardation layer laminate according to the present invention, whenexposed to heat, undergoes only a very small change in retardationvalue. Therefore, the laminate can be used even in the case where, afterthe incorporation of the retardation layer laminate, heat treatmentshould be carried out, for example, for the formation of an ITO film.This is advantageous in that the utilization range of the retardationlayer laminate according to the present invention can be greatlyexpanded.

A suitable retardation layer may be formed by dissolving the liquidcrystal material comprising a polymerizable liquid crystal monomer and aphotopolymerization initiator in a solvent to prepare a solution,coating the solution, and curing the coating. In this case, thepolymerizable liquid crystal monomer and the photopolymerizationinitiator may be those as described above.

The other construction is the same as described above, and, thus, thedescription thereof will be omitted.

<Circularly Polarized Light Controlling Optical Device>

In the present invention, when the optical device is a circularlypolarized light controlling optical device, the circularly polarizedlight controlling optical device may comprise a support and acholesteric layer provided on the support and formed by curing apolymerizable liquid crystal material while retaining cholestericregularity, wherein the percentage change in center reflectionwavelength of the cholesteric layer, when heated for 60 min at the sametemperature as the predetermined temperature in the heat treatment, isnot more than 5%, preferably not more than 3%, particularly preferablynot more than 1%.

Also in this case, since the change in layer thickness is associatedwith the change in center reflection wavelength of the cholestericlayer, when the optical device is used as a circularly polarized lightcontrolling optical device, the change in center reflection wavelengthcan be made very small even upon heating of an image display deviceusing the optical device in the production thereof.

In the circularly polarized light controlling optical device, asdescribed above, the change in center reflection wavelength upon heatingis so small that the circularly polarized light controlling opticaldevice according to the present invention can be used even in the casewhere, after the incorporation of the circularly polarized lightcontrolling optical device, for example, as a color filter, in an imageprocessing device, heat treatment should be carried out, for example,for the formation of an ITO film. This is advantageous in that theutilization range of the circularly polarized light controlling opticaldevice can be greatly expanded.

A suitable cholesteric layer in the circularly polarized lightcontrolling optical device may be formed by dissolving a liquid crystalmaterial comprising a polymerizable liquid crystal monomer, apolymerizable chiral dopant, and a photopolymerization initiator in asolvent to prepare a solution, coating the solution, and curing thecoating. In this case, the polymerizable liquid crystal monomer, thepolymerizable chiral dopant, and the photopolymerization initiator maybe those as described above.

The other construction is the same as described above, and, thus, thedescription thereof will be omitted.

<Heat Treatment Method>

The method for heat treating an optical device according to the presentinvention is characterized by heat treating an optical device,comprising a supporting substrate and an optical function layer providedon the supporting substrate and formed by curing a polymerizable liquidcrystal material while retaining predetermined liquid crystalregularity, at a temperature falling within a predetermined temperaturerange or by heat treating the optical device at or above a temperaturewhich corresponds to an isotropic layer before polymerizing thepolymerizable liquid crystal material, thereby imparting heat resistantto the optical device. In this case, preferably, the heat treatment iscarried out for 10 to 60 min. This heat treatment can move the liquidcrystal component or the chiral component, which remains uncured or doesnot form a satisfactory three-dimensional network structure, to a stablestate (position) within the layer.

In the method for heat treating an optical device according to thepresent invention, the heat treatment is previously carried out at apredetermined temperature, and impurities within the optical functionlayer are removed by this heat treatment. Therefore, even when heatingis carried out in a later stage, that is, even when, after mounting theoptical device subjected to the heat treatment according to the presentinvention, heating is carried out, for example, in an image processingdevice for the formation of a transparent electrode, since the heattreatment is previously carried out, there is no change in layerthickness of the optical device. Consequently, there is no fear ofcausing a change in various optical functions associated with the layerthickness. Thus, in mounting the heat treated optical device, forexample, on an image processing device, there is no restriction onmounting position and mounting timing. This offers an advantage that thedegree of freedom in the production of an image processing device andthe degree of freedom in product design can be significantly improved.

The production process of an optical device according to the presentinvention including the above heat treatment method will be described.

FIGS. 1 to 6 show an embodiment of the production process of an opticaldevice according to the present invention.

In this embodiment, a supporting substrate 3 having an aligning abilityis first provided. The supporting substrate 3 comprises a transparentsubstrate 1 and an aligning film 2 provided on the transparent substrate1 (step of providing supporting substrate, see FIG. 1).

Next, a coating liquid for liquid crystal layer formation prepared bydissolving a polymerizable liquid crystal material and aphotopolymerization initiator in a solvent is coated onto the supportingsubstrate 3 having an aligning ability, the coating is dried to removethe solvent, and the coating is kept at a temperature suitable fordeveloping a liquid crystal phase to form a liquid crystal layer 4 (stepof forming liquid crystal layer, see FIG. 2). By virtue of the action ofthe aligning film 2, the liquid crystal layer has liquid crystalregularity.

Upon the application of ultraviolet light 5 to the liquid crystal layer4 having liquid crystal regularity, the polymerizable liquid crystalmaterial in the liquid crystal layer is polymerized by radicalsgenerated from the photopolymerization initiator to convert the liquidcrystal layer 4 to an optical function layer 6 (step of forming opticalfunction layer, see FIGS. 3 and 4).

The optical device 8 comprising the optical function layer 6 provided onthe supporting substrate 3 is then kept, for example, in an oven at apredetermined temperature, whereby heat 7 is applied to the opticaldevice 8 for heat treatment (step of heat treatment, see FIG. 5).

The heat treated optical device 8 thus obtained has dimensionalstability against heat and, in its turn, is stable in various opticalfunctions (see FIG. 6).

The production process of an optical device according to the presentinvention will be described together with the detailed description ofthe heat treatment method according to the present invention.

1. Step of Providing Supporting Substrate

In the production of the optical device according to the presentinvention, a supporting substrate having an aligning ability should befirst provided. The supporting substrate having an aligning ability maybe constituted by a substrate which as such has an aligning ability.Alternatively, as shown in FIG. 1, the supporting substrate 3 having analigning ability may comprise an aligning film 2 provided on atransparent substrate 1. These are the same as those described above inthe column of <Optical device>, and the description thereof will beomitted.

2. Step of Forming Liquid Crystal Layer

In the present invention, as shown in FIG. 2, a liquid crystal layer 4is formed on the supporting substrate 3 having an aligning ability.

In the present invention, the liquid crystal layer is formed of apolymerizable liquid crystal material and is not particularly limited sofar as the liquid crystal layer can take liquid crystal phases havingvarious types of liquid crystal regularity.

The liquid crystal layer may be formed, for example, by the followingmethod. Specifically, a layer for liquid crystal layer formation isgenerally formed by dissolving a polymerizable liquid crystal material,such as a polymerizable monomer, and optional additives, such as achiral dopant and a photopolymerization initiator, in a solvent toprepare a coating liquid for liquid crystal layer formation and coatingthe coating liquid.

Coating methods usable herein include spin coating, roll coating, slidecoating, printing, dipping/pulling-up coating, and curtain coating (diecoating).

After the formation of the layer for liquid crystal layer formation, thesolvent is removed to form a liquid crystal layer having various typesof liquid crystal regularity. Methods usable for removing the solventinclude, for example, removal under reduced pressure or removal byheating, and a combination of these methods.

In the present invention, the method for forming a liquid crystal layeris not limited to the above method using the coating liquid for liquidcrystal layer formation. For example, a method may be adopted wherein adry film formed of a liquid crystal material is laminated on asupporting substrate having an aligning ability and the laminate is thenheated to impart liquid crystal regularity. In the present invention,however, for example, from the viewpoint of easy process, the abovemethod using the coating liquid for liquid crystal layer formation ispreferred.

The polymerizable liquid crystal material, the chiral dopant, and thephotopolymerization initiator used in the coating liquid for liquidcrystal layer formation are the same as those described above in thecolumn of <Optical device>, and the description thereof will be omitted.The solvent and other additives used in the coating liquid for liquidcrystal layer formation will be described.

<Solvent>

The solvent usable in the coating liquid for liquid crystal layerformation is not particularly limited so far as the solvent can dissolvethe polymerizable liquid crystal material and the like and is notdetrimental to the aligning ability on the supporting substrate havingan aligning ability.

The use of a single solvent sometimes results in unsatisfactorysolubility of the polymerizable liquid crystal material and the like or,as described above, results in the attack of the supporting substratehaving an aligning ability. The use of a mixture of two or moresolvents, however, can avoid such troubles. Suitable concentration ofthe polymerizable liquid crystal material in the solution variesdepending upon the solubility of the liquid crystalline composition andthe film thickness of the circularly polarized light controlling opticaldevice to be produced and thus cannot be unconditionally specified.However, the concentration of the polymerizable liquid crystal materialin the solution is generally in the range of 5 to 60% by mass.

A surfactant and the like may be added for coatability improvementpurposes to the coating liquid for liquid crystal layer formation.

The amount of the surfactant added is generally in the range of 0.01 to1% by mass based on the liquid crystalline composition contained in thesolution, although the amount of the surfactant added varies dependingupon the type of the surfactant, the type of the polymerizable liquidcrystal material, the type of the solvent, and the type of thesupporting substrate having an aligning ability to be coated with thesolution.

3. Step of Forming Optical Function Layer

In the present invention, upon the application of an actinic radiationto a liquid crystal layer, composed mainly of a polymerizable liquidcrystal material, formed in the step of forming a liquid crystal layer,the liquid crystal layer is cured in such a state that liquid crystalregularity is retained. Thus, optical function layers having variousoptical functions can be formed.

The actinic radiation applied at that time is not particularly limitedso far as the actinic radiation can polymerize the polymerizable liquidcrystal material, the polymerizable chiral dopant and the like. Ingeneral, however, light with a wavelength of 250 to 450 nm is applied.

The irradiation intensity may be properly regulated depending upon thecomposition of the polymerizable liquid crystal material constitutingthe liquid crystal layer and the amount of the photopolymerizationinitiator.

4. Step of Transfer

In the production process according to the present invention, ifnecessary, the step of transferring the optical function layer, providedon the supporting substrate having an aligning ability, onto a receivingobject may be provided after the step of forming an optical functionlayer.

The step of transfer may be carried out according to need, for example,in the case where the optical function layer is used in combination withother layer(s) or in the case where, although the optical function layeris preferably formed on a nonflexible supporting substrate, the opticalfunction layer is intended to be used in such a state that the opticalfunction layer is provided on the surface of a flexible film.

The transfer is carried out by bringing the surface of the receivingobject into contact with the surface of the optical function layerformed in the step of forming an optical function layer (see FIGS. 2 and3).

Transfer methods usable herein include, for example, a method wherein anadhesive layer is previously formed on the surface of the receivingobject or the surface of the optical function layer and the opticalfunction layer is transferred by taking advantage of the adhesive power,and a method wherein the aligning film or the like in the supportingsubstrate is rendered easily separable.

Further methods effective for the transfer include a method wherein theoptical function layer is formed so that the hardness of the surface ofthe optical function layer on its side, with which the receiving objectcomes into contact, is lower than the hardness of the surface of theoptical function layer on its supporting substrate side and the opticalfunction layer is transferred from this assembly onto the receivingobject, and a method wherein the optical function layer is formed sothat the percentage residual double bond in the surface of the opticalfunction layer on its receiving object side is higher than that in thesurface of the optical function layer on its supporting substrate sideand the optical function layer is transferred from this assembly ontothe receiving object. The degree of polymerization on the surface sideof the optical function layer can be made lower than that on thesubstrate side, for example, by using a photopolymerization initiator,which has such oxygen dependency that causes a lowering inpolymerization rate in the presence of oxygen, in the polymerizableliquid crystal material and conducting polymerization under conditionssuch that oxygen comes into contact with only the surface side of theoptical function layer.

The receiving object used in this step may be properly selecteddepending upon applications of the optical device. In general, however,the use of a transparent material, that is, a transparent substrate, issuitable.

This transparent substrate may be the same as that described in theabove column of “Supporting substrate having aligning ability,” and,thus, the description thereof will be omitted.

5. Step of Heat Treatment

The present invention is characterized in that the step of heattreatment is carried out after the step of forming an optical functionlayer, and the method for heat treating an optical device according tothe present invention includes the heat treatment method in this step.

Specifically, the heat treatment of the optical device according to thepresent invention is characterized in that the optical device comprisingthe support and the optical function layer provided on the support andformed in the step of forming an optical function layer is heat treatedat a predetermined temperature. As described above, when the support is,for example, a polymeric stretched film, the heat treatment temperatureis preferably in the range of about 80 to 120° C., more preferably inthe range of 90 to 120° C., still more preferably in the range of 90 to110° C. On the other hand, when the support is, for example, a glasssubstrate, the heat treatment temperature is preferably in the range ofabout 180 to 240° C., more preferably in the range of 190 to 230° C.,still more preferably in the range of 200 to 220° C.

The above temperature is generally determined by taking intoconsideration the heating temperature applied, for example, in theformation of an ITO electrode or in the formation of a polyimide film asan aligning film in the production of an image processing device.Specifically, stable film thickness and, in its turn, stable variousfunctions of the optical device associated with the film thickness atthe temperature applied in the production process of the imageprocessing device are required of the optical device to be heat treated.Accordingly, the heat treatment is preferably carried out at atemperature between at least the temperature applied in the productionprocess of an image processing device, to which the optical device isused, and a temperature at least 10° C. above the temperature applied inthe production process of the image processing device.

In the present invention, the heat treatment is carried out at the abovetemperature for 10 to 60 min, preferably 15 to 45 min, particularlypreferably 20 to 40 min.

The heat treatment time may be such that internal impurities can beremoved. From this viewpoint, the heat treatment is carried out for theabove time period range.

The heat treatment may be carried out in conventional heat treatmentequipment such as an oven.

In the present invention, the polymerizable liquid crystal materialpreferably contains a photopolymerization initiator. This is because, asdescribed above, the change in thickness of the optical function layerupon heating is minimized by preventing a lowering in the layerthickness caused by the removal of impurities having no chemical bond tothe main chain present within the optical function layer at the time ofheating. Therefore, when residues such as photopolymerization initiatorsare previously present within the optical function layer, the advantageof the heat treatment method according to the present invention can beutilized best.

The above heat treatment method is effective particularly in aretardation layer laminate wherein the optical function layer is aretardation layer. A change in thickness of the retardation layer uponheating in the production process of an image display device results ina significant change in retardation value of the retardation layer. Thechange in retardation value of the retardation layer disadvantageouslyposes a severe problem associated with optical design, and theretardation layer laminate, which causes a change in retardation value,cannot generally be used.

In the heat treatment method according to the present invention, byvirtue of the above previous heat treatment, the change in retardationvalue can be minimized even upon exposure of the retardation layer toheat, for example, in the production process of an image processingdevice. Therefore, in the production process, the optical device can beused even when heat is applied. This can advantageously significantlyexpand applications of the retardation layer laminate.

Further, the heat treatment method is also effective particularly for acircularly polarized light controlling optical device wherein theoptical function layer is a cholesteric layer. In this cholestericlayer, the center reflection wavelength depends upon the layerthickness. Therefore, in the cholesteric layer as with the retardationlayer, the center reflection wavelength, which is an important opticalproperty, does not undergo a change even upon heating in the productionof the circularly polarized light controlling optical device. This canadvantageously significantly expand applications of the circularlypolarized light controlling optical device.

It should be noted that the present invention is not limited to theabove embodiments. The above embodiments are illustrative only, andvariations and modifications fall within the technical scope of thepresent invention so far as they have substantially the sameconstruction as and the same function and effect as the technical ideadescribed in the claims of the present invention.

EXAMPLES

The following examples further illustrate the present invention.

A. Cholesteric Layer

(Preparation of Coating Liquid for Liquid Crystal Layer Formation)

A powder of a 100:5:5 (% by mass) mixture of a polymerizable liquidcrystal material, a chiral dopant, and a photopolymerization initiatorwas dissolved at a concentration of 30% by mass in toluene to prepare acoating liquid for liquid crystal layer formation. The polymerizableliquid crystal material, the chiral dopant, and the photopolymerizationinitiator used were as follows.

Polymerizable liquid crystal material: A polymerizable liquid crystalmonomer represented by formula (5) which has a polymerizable functionalgroup in its ends and exhibits nematic liquid crystallinity at 50 to100° C.

Chiral dopant: A polymerizable chiral dopant produced by attachingacrylate to both ends of a mesogen of a compound represented by formula(6) through a spacer to render the compound polymerizable

Photopolymerization initiator: IRG 907 (tradename, manufactured by CibaSpecialty Chemicals, K.K.)

(Formation of Aligning Film)

Next, a solution for the formation of an aligning film composed mainlyof polyimide was spin coated onto a 0.7 mm-thick glass substrate. Thesolvent was evaporated, and the coating was then post-baked at 200° C.,followed by rubbing by a conventional method to form an aligning film.

Separately, a solution for the formation of an aligning film composedmainly of polyvinyl alcohol was bar coated onto a 75 μm-thick TAC film.The solvent was evaporated, and the coating was then post-baked at 100°C., followed by rubbing by a conventional method to form an aligningfilm.

(Formation of Cholesteric Layer)

The above coating liquid for liquid crystal layer formation was spincoated onto the aligning film of the polyimide. The solvent was thenevaporated. Thereafter, liquid crystal molecules were aligned underconditions of 80° C. and 3 min, and selective reflection characteristicof a cholesteric structure could be confirmed. Ultraviolet light (UV)was then applied to the coating to cause polymerization, thereby forminga cholesteric layer. Thus, sample 1 was prepared.

Separately, the above coating liquid for liquid crystal layer formationwas bar coated onto the aligning film of polyvinyl alcohol. The solventwas then evaporated. Thereafter, liquid crystal molecules were alignedunder conditions of 80° C. and 3 min, and selective reflectioncharacteristic of a cholesteric structure could be confirmed.Ultraviolet light (UV) was then applied to the coating to causepolymerization, thereby forming a cholesteric layer. Thus, sample 2 wasprepared.

For sample 1 thus obtained, a part of the sample was heat treated at200° C. for 60 min, was then self-cooled to room temperature, and wasallowed to stand for one day (Example 1), while the other part of thesample was not heat treated (Comparative Example 1).

For sample 2 thus obtained, a part of the sample was heat treated at100° C. for 60 min, was then self-cooled to room temperature, and wasallowed to stand for one day (Example 2), while the other part of thesample was not heat treated (Comparative Example 2).

(Evaluation)

The sample of Example 1 and the sample of Comparative Example 1 weremeasured for selective reflection center wavelength, were then heated at200° C. for 60 min, and were again measured for selective reflectioncenter wavelength, and the percentage change in center wavelength, thatis, the percentage difference in center wavelength between the samplebefore the heat treatment and the sample after the heat treatment, wasdetermined. The results were as follows.

Example 1

1% Change to Shorter Wavelength Side

Comparative Example 1

6% Change to Shorter Wavelength Side

The sample of Example 2 and the sample of Comparative Example 2 weremeasured for selective reflection center wavelength, were then heated at100° C. for 60 min, and were again measured for selective reflectioncenter wavelength. The percentage change in center wavelength wasdetermined as described above. The results were as follows.

Example 2

1% Change to Shorter Wavelength Side

Comparative Example 2

6% Change to Shorter Wavelength Side

B. Retardation Layer 1

(Preparation of Coating Liquid for Liquid Crystal Layer Formation andFormation of Aligning Film)

A coating liquid for liquid crystal layer formation was prepared in thesame manner as in the above item A, except that any chiral dopant wasnot used and the mixing ratio of the polymerizable liquid crystalmaterial to the photopolymerization initiator was 100:5 (% by mass).Further, an aligning film was formed in the same manner as in the aboveitem A.

(Formation of Retardation Layer)

The coating liquid for liquid crystal layer formation was spin coated orbar coated on the above aligning film. The solvent was then evaporated.Thereafter, liquid crystal molecules were nematically aligned underconditions of 80° C. and 3 min. Ultraviolet light (UV) was then appliedto the coating to cause polymerization, thereby forming a retardationlayer 1. Thus, samples 3 and 4 were prepared.

For sample 3 having a nematic structure thus obtained, a part of thesample was heat treated at 200° C. for 60 min, was then self-cooled toroom temperature, and was allowed to stand for one day (Example 3),while the other part of the sample was not heat treated (ComparativeExample 3). Further, for sample 4 thus obtained, a part of the samplewas heat treated at 100° C. for 60 min, was then self-cooled to roomtemperature, and was allowed to stand for one day (Example 4), while theother part of the sample was not heat treated (Comparative Example 4).

(Evaluation)

The sample of Example 3 and the sample of Comparative Example 3 weremeasured for retardation value, were then heated at 200° C. for 60 min,and were again measured for retardation value, and the percentage changein retardation value, that is, the percentage difference in retardationvalue between the sample before the heat treatment and the sample afterthe heat treatment, was determined. The results were as follows.

Example 3

1% Change in Retardation Value

Comparative Example 3

6% Change in Retardation Value

The sample of Example 4 and the sample of Comparative Example 4 weremeasured for retardation value, were then heated at 100° C. for 60 min,and were again measured for retardation value. The percentage change inretardation value was determined in the same manner as described above.The results were as follows.

Example 4

1% Change in Retardation Value

Comparative Example 4

6% Change in Retardation Value

C. Retardation Layer 2

(Preparation of Coating Liquid for Liquid Crystal Layer Formation andFormation of Aligning Film)

A coating liquid for liquid crystal layer formation was prepared in thesame manner as in the above item A, except that the mixing ratio amongthe polymerizable liquid crystal material, the chiral dopant, and thephotopolymerization initiator was 100:15:5 (% by mass). Further, analigning film was formed in the same manner as in the above item A.

(Formation of Retardation Layer)

The coating liquid for liquid crystal layer formation was spin coated onthe aligning film of polyimide. The solvent was then evaporated.Thereafter, liquid crystal molecules were aligned under conditions of80° C. and 3 min. Ultraviolet light (UV) was then applied to the coatingto cause polymerization, thereby forming a cholesteric layer. Thus,sample 5 was prepared. Since the content of the chiral dopant componentin the above coating liquid for liquid crystal layer formation washigher than that in the coating liquid for liquid crystal layerformation used in Example 1, the selective reflection center wavelengthof the sample 5 thus prepared was in the ultraviolet region. Theretardation layer 2 thus formed could function as a negative phasedifference compensating plate.

The above coating liquid for liquid crystal layer formation was barcoated onto the aligning film of polyvinyl alcohol. The solvent was thenevaporated. Thereafter, liquid crystal molecules were aligned underconditions of 80° C. and 3 min. UV was then applied to the coating tocause polymerization, thereby forming a cholesteric layer. Thus, sample6 was prepared. Also for sample 6, the selective reflection centerwavelength was in the ultraviolet region.

For sample 5 having a cholesteric structure thus obtained, a part of thesample was heat treated at 200° C. for 60 min, was then self-cooled toroom temperature, and was allowed to stand for one day (Example 5),while the other part of the sample was not heat treated (ComparativeExample 5). Further, for sample 6 thus obtained, a part of the samplewas heat treated at 100° C. for 60 min, was then self-cooled to roomtemperature, and was allowed to stand for one day (Example 6), while theother part of the sample was not heat treated (Comparative Example 6).

(Evaluation)

The sample of Example 5 and the sample of Comparative Example 5 weremeasured for retardation value, were then heated at 200° C. for 60 min,and were again measured for retardation value, and the percentage changein retardation value, that is, the percentage difference in retardationvalue between the sample before the heat treatment and the sample afterthe heat treatment, was determined. The results were as follows.

Example 5

1% Change in Retardation Value

Comparative Example 5

6% Change in Retardation Value

The sample of Example 6 and the sample of Comparative Example 6 weremeasured for retardation value, were then heated at 100° C. for 60 min,and were again measured for retardation value. The percentage change inretardation value was determined in the same manner as described above.The results were as follows.

Example 6

1% Change in Retardation Value

Comparative Example 6

6% Change in Retardation Value

1. A method for heat treating an optical device, characterized bycomprising the step of heat treating, at a predetermined temperature, anoptical device comprising a supporting substrate and an optical functionlayer provided on the supporting substrate and formed by curing apolymerizable liquid crystal material while retaining predeterminedliquid crystal regularity, whereby heat resistance is imparted to theoptical device.
 2. A method for heat treating an optical device,characterized by comprising the step of heat treating an optical devicecomprising a supporting substrate and an optical function layer,provided on the supporting substrate and formed by curing apolymerizable liquid crystal material while retaining predeterminedliquid crystal regularity, at or above a temperature which correspondsto an isotropic layer before polymerizing the polymerizable liquidcrystal material, whereby heat resistance is imparted to the opticaldevice.
 3. The method according to claim 1, wherein the heat treatmentis carried out for 10 to 60 min.
 4. The method according to claim 1,wherein the polymerizable liquid crystal material contains aphotopolymerization initiator.
 5. The method according to claim 4,wherein the content of the photopolymerization initiator is not lessthan 1% by mass.
 6. The method according to claim 1, wherein the heattreatment is carried out at a temperature between a temperature appliedin the production process of an optical apparatus, in which the opticalfunction layer is used later, or the service temperature of the opticalapparatus and a temperature 10° C. above the temperature applied in theproduction process or the service temperature.
 7. The method accordingto claim 1, wherein the optical function layer is a retardation layer,the polymerizable liquid crystal material comprises a polymerizableliquid crystal monomer, and the liquid crystal regularity is nematicregularity, smectic regularity, or cholesteric regularity.
 8. The methodaccording to claim 1, wherein the optical function layer is acholesteric layer, the polymerizable liquid crystal material comprises apolymerizable liquid crystal monomer and a polymerizable chiral dopant,and the liquid crystal regularity is cholesteric regularity.
 9. Themethod according to claim 1, wherein the polymerizable liquid crystalmaterial comprises a polymerizable liquid crystal monomer and themolecule of the polymerizable liquid crystal monomer has a polymerizablefunctional group in its both ends.
 10. The method according to claim 9,wherein the polymerizable liquid crystal material comprises apolymerizable liquid crystal monomer and a polymerizable chiral dopantand the molecule of the polymerizable chiral dopant has a polymerizablefunctional group in its both ends.